Water Temperature Distribution Research Articles

Novel method for improving the cooling performance of natural draft wet cooling towers

A novel method for improving the cooling performance of natural draft wet cooling towers (NDWCTs) by installing air ducts in the rain zone was proposed for the first time. To study the effect of air ducts on NDWCTs and the associated mechanism, a 3D numerical model was established. The accuracy and credibility of the NDWCT model were validated. Based on the numerical model, the air temperature uniformity coefficient Cu,θ and the airflow rate G of the tower were computed to evaluate the effect of air ducts on tower aerodynamic field. The tower outlet water temperature t2 was assessed to clarify the effect of air ducts on tower cooling performance. This study found that air ducts improved both the aerodynamic field and the cooling performance of the NDWCT and that the improvement is quite dependent on the crosswind velocity. The optimal effect of air ducts achieved under windless conditions. To determine the effect mechanism of the air ducts, the distributions of air velocity, air-water ratio, air temperature, and water temperature on some representative sections of the tower were analyzed under both windless and crosswind conditions.

Using a nowcasting system to better understand lake water dynamics

AbstractConstraints in conventional field observations, such as measurement stations and instruments, human resources and occasional inclement weather conditions, hinder our understanding of the biological, chemical and physical processes in aquatic systems. Accordingly, the present study developed an integrated monitoring and prediction system called WISconsin nowCASTing (WIS‐CAST) to better predict spatial and temporal physical lake dynamics (e.g., water movements and temperatures). The system uses either present or past observations from instrumented buoys equipped with flow, water temperature and meteorological measurement sensors, integrating the observed data (i.e., in situ data) with high‐tech data communication tools, databases, a three‐dimensional hydrodynamic model and visualization tools. Acoustic Doppler current profiler in the system with radio wave two‐way communication covering a distance of 1,000 m also was utilized in the present study. The WIS‐CAST was deployed in early August 2006 in Trout Lake, a mid‐sized lake Wisconsin. It was maintained until late October 2006 as a local‐level, compacted nowcasting system to show temporal and spatial distributions of water temperature and movement in the water column and the entire lake. The lake dynamics affected by the Coriolis force for a state of summer stratification, a unique event of upwelling/downwelling and a process of overturn, all monitored and predicted during the measurement period with lake current and water temperature distributions, is presented herein. The WIS‐CAST, which was used as a system to assist lake management (e.g., water quality control), indicated the chemical dynamics were caused by a physical process, such as nutrient upwelling and vertical mixing of nutrients.

소형화된 피동응축용 냉각탱크 내 온도분포와 비등현상에 관한 실험적 연구

An experimental study was conducted to investigate the water temperature distribution and saturated boiling phenomenon in a small-scale passive condensate cooling tank that is part of an emergency passive auxiliary feedwater system used in nuclear power plants. During the heating process using an electric heater inserted in the tank, the temperature of water was measured at 36 locations. Isothermal line contours were generated based on the experimental data. The contours indicated that the water above the heater location had a nearly uniform temperature due to free convection flow. Conversely, a strong temperature gradient was observed in the water below the heater location. The bubble departure diameters at the cylindrical heater surface were measured using images captured by a high-speed camera. The diameters were observed to be within the range of values predicted using existing correlations.

Modeling and simulation of cross-flow transport membrane condenser heat exchangers

Transport Membrane Condenser (TMC) is a promising technology that works based on the capillary condensation property of the nano-scale ceramic porous membrane materials and can recover both waste heat and water in various industrial applications. For applications with high volume flow rate such as in power plants, a large number of TMC heat exchangers are required, which highlights the importance of the optimum design for the TMC exchangers in order to obtain the maximum heat transfer and minimum cost of the TMC heat exchanger unit. In this paper, the effects of different tube spacing and the inlet water vapor mass fraction on the overall performance of a membrane-based heat exchanger have been studied numerically using a combined condensation model based on the capillary condensation and condensation on a solid wall. The results were obtained in terms of the Euler number, dimensionless volumetric heat transfer density, and contours of the water mass fraction and temperature distribution inside the TMC heat exchanger.

Water temperatures in the headwaters of the Volga River: Trend analyses, possible future changes, and implications for a pan‐European perspective

AbstractWater temperature is a physical property influencing abiotic and biotic parameters in an aquatic ecosystem. In different Central European rivers and lakes, a general trend of water temperatures in the range of +0.05 to +0.8 °C per decade was identified. Our case study analyses whether similar patterns apply to the headwaters of the Volga River, in the East European plain. Based on a dataset of water temperatures for 2008–2015, we investigated the spatial and temporal distribution of water temperature along the Tudovka River and estimated backward as well as predicted future changes from development scenarios throughout the 21st century. Stochastic models were applied to track trends and variations in water temperature. Furthermore, the correlation between water temperature and air temperatures was used to model historical water temperatures and to predict possible changes in the future, under the effects of climate change. Based on climate change scenarios, an increase of the mean water temperatures as well as changes regarding the ice cover can be expected until the end of this century. The conditions described for the headwaters of the Volga River system represent a valuable dataset for medium and large rivers in the East European plain and serve as a basis for future management.

Modeling of thermodynamics of ice and water in seasonal ice-covered reservoir

A width-averaged 2-D numerical model for simulating vertical distributions of flow and water temperature in reservoirs with an ice cover is developed. In this model, the 2-D flow and water temperature distributions are solved by the finite volume method with the k-e turbulent model. The heat conduction in the ice cover is modeled by the vertical heat transfer and the heat exchanges through the air-ice and ice-water interfaces. The model is applied to a 153 km long reservoir in Songhua River and the simulated results are in a good agreement with the field data of both the vertical water temperature and the ice thickness. The simulated results show that the ice cover thickness in the reservoir is not uniform, the maximum thickness appears in the middle reach, the outflow temperature has an obvious variation as compared with the natural temperature, and a buoyant flow occurs in the reservoir surface at the freeze-up and break-up periods. The model can effectively simulate the water temperature and the ice conditions of large reservoirs in cold regions.

Effect analysis on boiling heat transfer performance of an internal combustion engine at the shutdown time

In this paper, a liquid-solid coupling simulation of circulated coolant fluid and solid body of an internal combustion engine is carried out using AVL-FIRE software. Contrary to the previous numerical studies, unsteady simulations are performed in the present work. A validation test against experimental data is examined using BDL and Chen correlations. The results show that two correlations give reasonable results for the used setup at engine operating temperature. The effect of pressure, heat transfer coefficient in water jacket and temperature distribution in block and cylinder head is studied. In addition, the influence of engine shutdown on temperature distribution in water jacket, block and cylinder head is investigated. The results demonstrate that the boiling heat flux is zero until the shutdown time, then increases suddenly and reaches a maximum value between the two cylinders.

Numerical study of droplet evaporation in an acoustic levitator

We present a finite element method for the simulation of all relevant processes of the evaporation of a liquid droplet suspended in an acoustic levitation device. The mathematical model and the numerical implementation take into account heat and mass transfer across the interface between the liquid and gaseous phase and the influence of acoustic streaming on this process, as well as the displacement and deformation of the droplet due to acoustic radiation pressure. We apply this numerical method to several theoretical and experimental examples and compare our results with the well-known d2-law for the evaporation of spherical droplets and with theoretical predictions for the acoustic streaming velocity. We study the influence of acoustic streaming on the distribution of water vapor and temperature in the levitation device, with special attention to the vapor distribution in the emerging toroidal vortices. We also compare the evaporation rate of a droplet with and without acoustic streaming, as well as the evaporation rates in dependence of different temperatures and sound pressure levels. Finally, a simple model of protein inactivation due to heat damage is considered and studied for different evaporation settings and their respective influence on protein damage.

Numerical investigation on residence time of cooling water and surface temperature distribution of water-cooled grates

Waste incineration is a treatment system that reduces waste volume while capturing or destroying potentially harmful substances and recovers energy and chemical contents from wastes. Grate incinerator is one of the thermal treatment methods in waste incinerations. The incineration grates are exposed to high heat flux due to the occurrence of combustion on their surface. Therefore, cooling the incineration grate is one of the main issues in these treatments. In this study, the conjugate heat transfer between the cooling water and incineration grate is investigated numerically. We consider different geometries of the internal guide vane in the cooling channel and analyze the effects of the shapes of the guide vane on the heat transfer performance in the incineration grate. We also calculate the fluid residence time in the cooling channel and investigate the relation between the heat transfer performance and residence time of the cooling fluid. Results confirm that the maximum residence time of the cooling fluid can be reduced, from which the heat transfer performance can be improved.

Experimental and numerical investigations of heat transfer and thermal efficiency of an infrared gas stove

An infrared gas stove is a low-pressure gas stove type and it has higher thermal efficiency than the other domestic cooking stoves. This study considers the computationally determine water and air temperature distributions, water and air velocity distributions and thermal efficiency of the infrared gas stove. The goal of this work is to investigate the effect of various pot diameters i.e. 220 mm, 240 mm and 260 mm on the water and air temperature distributions, water and air velocity distributions and thermal efficiency of the infrared gas stove. The time-dependent heat transfer equation involving diffusion and convection coupled with the time-dependent fluid dynamic equation is implemented and is solved by using the finite element method (FEM). The computer simulation study is validated with an experimental study, which is use standard experiment by LPG test for low-pressure gas stove in households (TIS No. 2312-2549). The findings revealed that the water and air temperature distributions increase with greater heating time, which varies with the three different pot diameters (220 mm, 240 mm and 260 mm). Similarly, the greater heating time, the water and air velocity distributions increase that vary by pot diameters (220, 240 and 260 mm). The maximum water temperature in the case of pot diameter of 220 mm is higher than the maximum water velocity in the case of pot diameters of 240 mm and 260 mm, respectively. However, the maximum air temperature in the case of pot diameter of 260 mm is higher than the maximum water velocity in the case of pot diameters of 240 mm and 220 mm, respectively. The obtained results may provide a basis for improving the energy efficiency of infrared gas stoves and other equipment, including helping to reduce energy consumption.

Analysis of the effect of water steam concentration on water drop cooling process efficiency in conditions of water cooling towers of thermal power plants

Numerical investigation of transient distribution of temperature in water drops cooled in cool blast in conditions typical for high capacity evaporative water cooling towers has been done. Water drops cooling through thermal conductivity and water evaporation has been taken into consideration. It has been proved that the analysis of temperature distribution along the radius of water drop increases reliability of evaluation results of average temperature of water drops when they are cooled. Effect of water steam concentration in steam-gas mixture layer surrounding a water drop on water cooling towers efficiency has been evaluated.

Study of Marine Waters Hydrological Characteristics in Odessa Bay in 2016-2017

Purpose. The results of pilot monitoring project carried out in Odessa Bay coastal waters in 2016-2017 by a research group of the Regional Center for Integrated Monitoring and Environmental Studies (Odessa National I.I. Mechnikov University) have been summarized. Methods. Primary data on transparency, temperature and salinity of marine water have been collected using standard methods. Data processing, calculation of statistics, producing of graphs and maps have been carried out using ArcGIS and Excel software. Results. Temporal and spatial distributions of transparency, temperature and salinity of marine coastal waters of Odessa Bay in the area of Marine Hydrobiological Station of the University for the period from April 2016 to August 2017 have been presented and analyzed. Using the results of analysis of the accumulated experimental data on transparency, temperature and salinity of seawater the peculiarities of those characteristics’ seasonal changes have been revealed. It was demonstrated that marine water transparency was minimal in May and June 2016 (2.2-2.8 m); maximal transparency values for the entire period of observation (7.0 m) was registered in May 2017. A strongly pronounced seasonal variation was revealed in the distribution of marine water temperature in Odessa Bay in 2016-2017, which was determined by spring-summer warming up / autumn-winter cooling down, as well as coastal upwelling, advection of water masses from other marine areas. It was shown that with observations performed every 10 days the desalinated water masses were registered in 13.5% of measurements but never found during monthly surveys at 13 of the micro-polygon. It means that during the detailed monthly surveys in Odessa Bay coastal waters all the cases of advection of desalinated water stayed unregistered. Conclusions. Impact of transformed water masses from the Dnieper-Bug mouth on seasonal cycles of hydrological characteristics in Odessa Bay in 2016-2017 has been established. Violations of the seasonality of thermohaline structure formation in Odessa Bay waters in 2016–2017 due to the longshore cyclonic and compensatory currents impact in the coastal zone have been recorded. Forming of stable two-layer vertical density stratification in Odessa Bay coastal waters at the spring and summer periods of 2016-2017 has been traced.

Tolerance of Prenant's Schizothoracin Schizothorax prenanti to Total Dissolved Gas Supersaturated Water at Varying Temperature

AbstractHydropower development changes the temporal and spatial distribution of water temperature and causes total dissolved gas (TDG) supersaturation downstream of dams. We conducted laboratory experiments to determine the effects of TDG supersaturation on Prenant's Schizothoracin Schizothorax prenanti at varying water temperatures. The fish were exposed to 120, 130, 135, and 140% TDG‐supersaturated water at different water temperatures within the range of 12–24°C for 96 h. Survival rate of Prenant's Schizothoracins declined with increasing TDG saturation. At 120% TDG, the final survival rate of fish was over 50% at the different temperatures. However, when the TDG level increased to 130% or above, the survival rate decreased sharply. The median survival time of fish ranged from 5.22 to 18.62 h when exposed to 130% TDG, ranged from 2.41 to 9.41 h at 135% TDG, and was less than 5 h at 140% TDG. Under 120% TDG conditions, fish survival rate was not significantly different among water temperatures (12–24°C). However, when the TDG level was 130%, the survival rate of the fish declined with increasing water temperature. In 135% and 140% TDG‐supersaturated water, the survival time of the fish was longer at 16°C than at other temperatures.

Density Dependence, Landscape, and Weather Impacts on Aquatic Aedes japonicus japonicus (Diptera: Culicidae) Abundance Along an Urban Altitudinal Gradient.

The Asian Bush Mosquito, Aedes (Finlaya) japonicus japonicus (Theobald) is an important globally invasive mosquito species. In comparison with other major invasive mosquitoes, relatively little is known about Ae. j. japonicus population dynamics in the field. Here, we present results from a 54-biweek long study of Ae. j. japonicus abundance in ovitraps set across the altitudinal gradient of Mt. Konpira, Nagasaki, Japan. Spatially, we found that Ae. j. japonicus fourth instar larvae (Aj4il) were more abundant at the base and top of Mt. Konpira and in ovitraps with more platykurtic water temperature (WT) distributions. In contrast, we found that temporally Aj4il were more abundant when ovitrap WT was more leptokurtic with 2 weeks of lag, and with high relative humidity SD with 2 months of lag. We also found that Aj4il were unlikely present when ovitrap WT was below 12.41°C. Parameter estimates for the Ricker model suggested that Ae. j. japonicus population growth was under density-dependence regulation, with a stable population dynamics whose fluctuations were associated with changes in ovitrap WT kurtosis and demographic stochasticity. Our results suggest that Aj4il abundance is more sensitive to temperature changes in kurtosis than mean values, potentially limiting the predictive ability of Ae. j. japonicus niche models based on the increase of average temperatures with global warming, and suggesting this mosquito species has a relatively coarse-grained response to temperature changes.

Mechanism of flow reversal during solidification of an anomalous liquid

In a wide variety of fluidic systems involving thermal and compositional gradients, local density changes lead to the onset of natural convection that influences the process itself, for example, during phase-change phenomena and magmatic flows. Accurate knowledge of the flow characteristics is essential to quantify the impact of the flow of the processes. In this work, the first-ever demonstration of flow reversal during bottom-up solidification of water using full-field thermal and flow measurements and its direct impact on the solidifying interface is presented. Based on prior optical interferometric measurements of full-field temperature distribution in water during solidification, we use the particle image velocimetry technique to quantify and reveal the changing natural convection pattern arising solely due to the density anomaly of water between 0 °C and 4 °C. The independently captured thermal and flow fields show striking similarities and clearly elucidate the plausible mechanism explaining the formation of a curved interface at the stagnation point and the subsequent reversal of flow direction due to a changed interface morphology. A control volume analysis is further presented to estimate the energy invested in the formation of a perturbation and the resulting flip in the flow direction caused by this perturbation.

Simulation and performance analysis on condenser coil in household heat pump water heater

A numerical investigation of performance analysis on heat pump water heater (HPWH) was carried out. In this study, a coupling model containing both vapor-compression cycle and water heater was established, in which model of vapor-compression cycle was developed in MATLAB to obtain the heat flux boundary condition for helically coil and then the two-dimensional flow and heat transfer of water tank was simulated by CFD. Water temperature distribution, heat transfer coefficient and COP were three main characteristics to evaluate the performance of HPWH. The results of the coupling simulation showed good agreement with experimental results. Then with help of this coupling model, system performance of variable-diameter coil and constant-diameter coil were compared. Results indicated that heat transfer coefficient of variable-diameter coil was 19.06% higher and average COP was 3.97% higher for this coil type. Hence, it was found that by reducing coil pitch and properly designing coil diameter, maximum temperature difference in altitude direction was no more than 3°C, average water temperature was about 1°C higher and Nuw,d was at least 3.05% higher. This work could provide some guideline on optimization of condenser coil designs.

Measurements of crosswind influence on a natural draft dry cooling tower for a solar thermal power plant

Crosswind is a significant concern for natural draft dry cooling towers. The concern is more serious for shorter towers. Therefore, the crosswind influence is a significant threat to the use of natural draft dry cooling towers in concentrating solar thermal power plants, which are generally built at sizes smaller than conventional fossil-fired plants and employ relatively shorter towers. While some numerical studies and small lab-scale test reports exist, very few full scale experimental studies have been reported for conventional cooling towers and none for relatively short cooling towers suitable for renewable thermal power plants. To address this gap, a 20-m tall fully instrumented natural draft dry cooling tower was built by the University of Queensland. The tower was designed to serve a future 1-MWe concentrating solar thermal plant on the same site. Its performance was tested under different ambient temperatures and crosswind speeds. The detailed experimental data of the crosswind condition, air temperature distribution inside and outside of the cooling tower and the cooling performance are presented. The experimental data demonstrate the substantial yet complex impact of the crosswind on cooling tower performance. Significant non-uniformities in air and hot water temperature distributions and strong air vortices inside the tower were observed in high crosswind speeds. Unlike tall cooling towers used in large conventional plants, the cooling tower performance does not monotonously decrease with the increase of the crosswind speed. In fact, after the tower performance drops to its lowest level at a wind speed around 5 m/s, the trend is reversed and further increases in the crosswind speed help the tower performance. Analysis shows that this reversal occurs because the tower heat transfer mechanism changes. As crosswind rises above the critical speed, the airflow inside the cooling tower becomes increasingly controlled by the crosswind instead of the natural draft.

Experimental study on heat transfer enhancement caused by the flow-induced vibration of a prism inside a channel

An experimental study, using water as the working fluid, has been performed to analyze whether a passive system based on flow-induced vibration is a feasible option to enhance heat transfer in the laminar confined regime. The experimental setup consisted of a 1.5m tall vertical channel manufactured on methacrylate (square cross-section of 25mm×25mm) and a tethered square section buoyant prism (10mm×10mm×25mm) placed inside the channel. The tethered prism was allowed to move freely (like an inverted pendulum) as a consequence of its interaction with the incoming flow. An aluminum block placed in the channel walls around the prism heated the water with a constant wall temperature of 60C. The flow Reynolds number (Re) based on the prism cross section length was varied between 80 and 800. Three prisms with three different prism-to-water density ratios (m∗) were used in the experiments: 0.56, 0.70 and 0.91. The case with the prism anchored to the walls was considered also. Regarding heat transfer, all cases were compared to the reference case which consisted of the clean channel with no prism present. The flow velocity was characterized using a Particle Image Velocimetry System. The electric power supply to the heated walls was recorded and the spatial distribution of water temperature was measured in a transversal plane downstream of the heated walls. It was found that the heat transfer enhancement provided by this system, as compared to the clean channel with no prism present, was very much dependent on Re. For example, at the lowest Re 80, the improvement on the Nusselt number (Nu) was negligible for all cases. At highest Re 800, the improvement on Nu was 100% for the case of prism-to-water density ratio of 0.91, and 66% for the case of the prism anchored to the walls. This suggests that, when thinking of practical engineering applications, passive systems based on flow-induced vibration might represent a feasible alternative, because of its simplicity, to active systems that require a more complex implementation that includes a motor to move the prism. The simplest setup (the prism anchored to the walls) also yields a significant, if smaller, heat transfer enhancement.

Modelling the plankton groups of the deep, peri-alpine Lake Bourget

Predicting phytoplankton succession and variability in natural systems remains to be a grand challenge in aquatic ecosystems research. In this study, we identified six major plankton groups in Lake Bourget (France), based on cell size, taxonomic properties, food-web interactions and occurrence patterns: cyanobacterium Planktothrix rubescens, small and large phytoplankton, mixotrophs, herbivorous and carnivorous zooplankton. We then developed a deterministic dynamic model that describes the dynamics of these groups in terms of carbon and phosphorus fluxes, as well as of particulate organic phosphorus and dissolved inorganic phosphorus. The modular and generic model scheme, implemented as a set of modules under Framework for Aquatic Biogeochemical Models (FABM) enables run-time coupling of the plankton module an arbitrary number of times, each time with a prescribed position across the autotrophy/heterotrophy continuum. Parameters of the plankton groups were mainly determined conjointly by the taxonomic and allometric relationships, based on the species composition and average cellular volume of each group. The biogeochemical model was coupled to the one-dimensional General Ocean Turbulence Model (GOTM) and forced with local meteorological conditions. The coupled model system shows very high skill in predicting the spatiotemporal distributions of water temperature and dissolved inorganic phosphorus for five simulated years within the period 2004 to 2010, and intermediate skill in predicting the plankton succession. We performed a scenario analysis to gain insight into the factors driving the sudden disappearance of P. rubescens in 2010. Our results provide evidence for the hypothesis that the abundance of this species before the onset of stratification is critical for its success later in the growing season, pointing thereby to a priority effect.

Effect of design configurations on water flow window performance

Water flow window has very good application potential in zero carbon buildings of the warm climate. In this study, the effects of water-flow window configurations were investigated, such as the water layer thickness and glazing height-to-width ratio (GHTWR). The effects of distribution header design on the thermal and flow characteristics were also analyzed. Its long-term dynamic thermal performance was examined through a self-developed simulation program, of which the FORTRAN code was previously validated through comparison with experimental data. In the current study, the one-dimensional thermal simulation modelling approach was further justified through CFD analysis. Then the overall thermal performance of the window system was evaluated from the aspects of useful water heat gain and the impact on space air-conditioning power consumptions. A water layer of thickness around 15–20 mm and a GHTWR of 0.4 were found desirable for the tested cases. While the size and distribution of the header openings would affect the localized water flow and temperature distribution, their effect on the laminar upward flow and the final temperature rise is not significant.